The present invention provides a system and method for performing electrosurgical cutting, ablation (volumetric tissue vaporization), coagulating or modification within a body tissue, cavity or vessel on the surface of a patient. The system and method of the invention herein disclosed may be used in relatively dry environments for, for instance, oral, otolaryngological, laparoscopic, and dermatologic procedures.
Electrosurgical procedures require a proper electrosurgical generator, which supplies the Radio Frequency (RF) electrical power, and a proper surgical electrode (also known as an electrosurgical probe). Under appropriate conditions the desired surgical effects are accomplished.
Note: in common terminology and as used herein the term “electrode” may refer to one or more components of an electrosurgical device (such as an active electrode or a return electrode) or to the entire device, as in an “ablator electrode”. Electrosurgical devices may also be referred to as “probes”.
Electrosurgical procedures rely on the application of RF electrical power using an electrode (or probe) for cutting, ablation or coagulation of tissue structures in a joint space which is filled by liquid. Many types of electrosurgical devices can be used; however, they can be divided to two general categories: monopolar devices and bipolar devices. When monopolar electrosurgical devices are used, the RF current generally flows from an exposed active electrode, through the patient's body, to a passive, return current electrode that is externally attached to a suitable location on the patient body. In this way the patient's body is part of the return current circuit. When bipolar electrosurgical devices are used, both the active and the return current electrodes are exposed, and are typically positioned in close proximity to each other and the active site. The RF current flows from the active electrode to the return electrode, through the nearby tissue and conductive fluids. Monopolar and bipolar devices in many fields of electrosurgery operate according to the same principles.
During the last several years, specialized arthroscopic electrosurgical probes called ablators have been developed. Examples of such instruments include ArthroWands manufactured by Arthrocare (Sunnyvale, Calif.), VAPR electrodes manufactured by Mitek Products Division of Johnson & Johnson (Westwood, Mass.) and electrodes by Stryker Corporation (Kalamazoo, Mich.) and Smith and Nephew Endoscopy (Andover, Mass.). These ablators differ from conventional electrosurgical probes in that they are designed for the bulk removal of tissue by vaporization in a conductive liquid environment, rather than for the cutting of tissue or for coagulation of bleeding vessels.
Recently the use of electrosurgery with conductive fluids for urology, gynecology and other procedures is also becoming popular. Previously, mostly non-conductive fluids were used for these applications.
While standard electrodes are capable of ablation (bulk vaporization), their geometries are not efficient for accomplishing this task. During ablation, water within the target tissue is vaporized. Because volumes of tissue are vaporized rather than discretely cut out and removed from the surgical site, the power requirements of ablator electrodes are generally higher than those of other arthroscopic electrosurgical electrodes. The geometry and design of the electrode and the characteristics of the RF power supplied to the electrode greatly affect the power required for ablation (vaporization) of tissue. Electrodes with inefficient designs require higher power levels than those with efficient designs.
During electrosurgery procedures in conductive fluids, most of the RF energy delivered to an electrode is dissipated in the fluid and in the adjacent tissue as heat, thereby raising the temperature of the fluid within the cavity and of the adjacent tissue. A substantial fraction of the RF power is used for the creation of sparks (arcs) in the vicinity of the electrodes. These sparks accomplish the tissue vaporization and cutting. In summary, the sparks are essential for tissue vaporization (ablation), while heating of the liquid and tissue away from the active electrode tip always occurs but has no desirable clinical effect.
The heating of the irrigation fluid and especially the adjacent tissue is not beneficial to the patient. On the contrary, this may substantially increase the likelihood of patient burns. For this and other reasons, improved, efficient electrosurgical electrodes are desirable for tissue vaporization and cutting of tissue structures.
An electrosurgical probe, in general, is composed of a metallic conductor surrounded by a dielectric insulator (e.g., formed of plastic, ceramic or glass) along the length, with the exception of the exposed metallic electrode. The probe electrode is often immersed in a conducting fluid, either filling a natural or created cavity or applied as irrigant to a “dry” site, and is brought in contact with the tissue structure during the electrosurgical procedure. The probe is energized, typically at a voltage of few hundred to a few thousand volts, using an RF generator operating at a frequency between 100 kHz to over 4 MHz. This voltage induces a current in the conductive liquid and nearby tissue. This current heats the liquid and tissue, the most intense heating occurring in the region very close to the electrode where the current density is highest. At points where the current density is sufficiently high, the liquid boils locally and many steam bubbles are created, the steam bubbles eventually insulating part or all of the electrode. Electrical breakdown in the form of an arc (spark) occurs in the bubbles which insulate the electrode. The sparks in these bubbles are channels of high temperature ionized gas, or plasma (temperature of about a few thousand degrees Kelvin). These high current density sparks, heat, evaporate (ablate) or cut the tissue (depending on the specific surgical procedure and the probe geometry) that is in contact with the spark.
The spark generation and tissue heating, modification or destruction very close to the electrode tip are a beneficial and desirable effect. At the same time, the induced current heats liquid and tissue farther away from the immediate vicinity of the electrode tip. This heating is undesirable and potentially dangerous because it may uncontrollably damage tissue structures in surrounding areas and also deep under the surface. The design of higher efficiency probes is desirable as it would lead to less heating of fluid and tissue not in close proximity, and give the surgeon a larger margin of safety during the procedure.
Ablation (vaporizing) electrodes currently in use, whether monopolar or bipolar, have an active electrode surrounded by an insulator significantly larger in size than the ablating surface of the electrode. For ablators with a circular geometry, the diameter of the portion of the probe which generates ablative arcs (the “working” diameter) is generally not greater than 70 to 80 percent of the diameter of the insulator (the “physical” diameter) and therefore only about 50% of the physical probe area can be considered effective. This increases the size of the distal end of the electrode necessary to achieve a given ablative surface size, and, for some procedures performed in internal body cavities, necessitates the use of large bore cannulae, an undesirable condition.
Many surgical procedures are not performed inside a natural or formed body cavity and as such are not performed on structures submerged under a conductive liquid. In laparoscopic procedures, for instance, the abdominal cavity is pressurized with carbon dioxide to provide working space for the instruments and to improve the surgeon's visibility of the surgical site. Other procedures, such as oral surgery, the ablation and necrosis of diseased tissue, or the ablation of epidermal tissue, are also typically performed in an environment in which the target tissue is not submerged. In such cases, it is necessary to provide a conductive irrigant to the region surrounding the active electrode(s), and frequently also to aspirate debris and liquid from the site. Such irrigant may be applied by a means external to the instrument; however, having an irrigation means internal or attached to the instrument generally provides better control and placement. This is also true for aspiration of fluid and debris. External means may be used for aspiration from the site; however, aspiration through the instrument distal end provides improved fluid control and may, in some cases, draw tissue toward the active electrode thereby enhancing performance.
Electrosurgical devices having means for irrigating a site, and/or means for aspirating fluid, bubbles and debris from a site are well known. Smith, in U.S. Pat. No. 5,195,959, disclose an electrosurgical device with suction and irrigation. Bales, et al., in U.S. Pat. No. 4,682,596 disclose a catheter for electrosurgical removal of plaque buildup in blood vessels, the catheter having lumens for supplying irrigant to the region of the instrument distal tip and for aspirating debris from the region. Hagen, in U.S. Pat. No. 5,277,696, discloses a high frequency coagulation instrument with means for irrigation and aspiration from the region of the instrument tip. Pao, in U.S. Pat. No. 6,674,499, discloses a coaxial bipolar probe with suction and/or irrigation. Eggers, in U.S. Pat. No. 6,066,134, discloses a method for electrosurgical cutting and coagulation which uses a bipolar probe having means for irrigating and aspirating from the region of the probe distal tip. The Eggers device uses the irrigant flow to provide a return path to a return electrode recessed axially a distance away from the active electrode(s).
The placement and volume of aspiration flow through an electrosurgical instrument in the region of an active electrode, or even through the active electrode, may adversely affect the performance of the instrument. Electrosurgery, particularly procedures in which tissue is vaporized, is a thermal process. Aspiration which draws fluid through or around the active electrode surfaces draws away process heat, thereby decreasing heating of the conductive irrigant in the region so as to decrease bubble production and ablative arcing. This makes the device less efficient thereby requiring increased power to achieve acceptable performance.